This application discloses a process for producing high molecular weight hydrocarbons from a lower olefin feedstock by employing a shape selective crystalline silicate catalyst which is surface inactivated.
Recent work in the field of olefin upgrading has resulted in a catalytic process for converting lower olefins to heavier hydrocarbons. Heavy distillate and lubricant range hydrocarbons can be synthesized over certain medium pore, shape-selective zeolite catalysts at elevated temperature and pressure to provide a product having substantially linear molecular conformations due to the ellipsoidal shape selectivity of such catalysts.
Conversion of olefins to gasoline and/or distillate products is disclosed in U.S. Pat. Nos. 3,960,978 and 4,021,502 (Givens, Plank and Rosinski) wherein gaseous olefins in the range of ethylene to pentene, either alone or in admixture with paraffins are converted into an olefinic gasoline blending stock by contacting the olefins with a catalyst bed made up of ZSM-5 zeolite. Such a technique has been developed by Garwood, et al, as disclosed in European Patent Application No. 83301391.5, published 29 Sept. 1983. In U.S. Pat. Nos. 4,150,062; 4,211,640; 4,227,992; and 4,547,613 Garwood, et al disclose operating conditions for a process for selective conversion of C.sub.3 .sup.+ olefins to mainly aliphatic hydrocarbons.
In the process for catalytic conversion of olefins to heavier hydrocarbons by catalytic oligomerization using a medium pore shape selective acid crystalline zeolite, process conditions can be varied to favor the formation of hydrocarbons of varying molecular weight. At moderate temperature and relatively high pressure, the conversion conditions favor C.sub.10 .sup.+ aliphatic product. Lower olefinic feedstocks containing C.sub.2 -C.sub.8 alkenes may be converted; however, the distillate mode conditions do not convert a major fraction of ethylene. A typical reactive feedstock consists essentially of C.sub.3 -C.sub.6 mono-olefins, with varying amounts of non-reactive paraffins and the like being acceptable components.
Shape-selective oligomerization, as it applies to the conversion of C.sub.2 -C.sub.10 olefins over ZSM-5, may produce higher olefins up to C.sub.30 and higher. As reported by Garwood in "Intrazeolite Chemistry 23", (Amer. Chem. Soc., 1983), reaction conditions favoring higher molecular weight product are low temperature (200.degree.-260.degree. C.), elevated pressure (about 2000 kPa or greater), and long contact time (less than 1 WHSV). The reaction under these conditions proceeds through the acid-catalyzed steps of (1) oligomerization, (2) isomerization-cracking to a mixture of intermediate carbon number olefins, and (3) interpolymerization to give a continuous boiling product containing all carbon numbers. The channel systems of medium pore catalysts impose shape-selective constraints on the configuration of the large molecules, accounting for the differences with other catalysts.
The desired oligomerization-polymerization products include c.sub.10 .sup.+ substantially linear aliphatic hydrocarbons. This catalytic path for propylene feed provides a long chain which generally has lower alkyl (e.g., methyl) substituents along the straight chain.
The final molecular configuration is influenced by the pore structure of the catalyst. For the higher carbon numbers, the structure is primarily a methyl-branched straight olefinic chain, with the maximum cross-section of the chain limited by the dimension of the largest zeolite pore. Although emphasis is placed on the normal 1-alkenes as feedstocks, other lower olefins, such as 2-butene or isobutylene, are readily employed as starting materials due to rapid isomerization over the acidic zeolite catalysts. At conditions chosen to maximize heavy distillate and lubricant range products (C.sub.20 .sup.+), the raw aliphatic product is essentially mono-olefinic. Overall branching is not extensive and may occur at spaced positions within the molecule.
The viscosity index of a hydrocarbon lube oil is related to its molecular configuration. Extensive branching in a molecule usually results in a low viscosity index. It is believed that two modes of oligomerization/polymerization of olefins can take place over acidic zeolites, such as HZSM-5. One reaction sequence takes place at Bronsted acid sites inside the channels or pores, producing essentially linear materials. The other reaction sequence occurs on the outer surface, producing more branched material. By decreasing the surface acid activity of such zeolites, fewer highly branched products with low VI are obtained.
Several techniques may be used to increase the relative ratio of intra-crystalline acid sites to surface active sites. This ratio tends to increase with crystal size due to geometric relationship between volume and superficial surface area. Deposition of carbonaceous materials by coke formation can also shift the effective ratio, as disclosed in U.S. Pat. No. 4,547,613.
Dealumination of zeolite surfaces can also reduce surface activity. Conventional techniques for zeolite dealumination include hydrothermal treatment, mineral acid treatment with HCl, HNO.sub.3, and H.sub.2 SO.sub.4, and chemical treatment with SiCl.sub.4 or EDTA. The treatments are limited, in many cases, in the extent of dealumination by the onset of crystal degradation and loss of sorption capacity. U.S. Pat. No. 4,419,220 to LaPierre et al discloses that dealumination of zeolite Beta via treatment with HCl solutions is limited to SiO.sub.2 /Al.sub.2 O.sub.3 ratios of about 200 to 300 beyond which significant losses to zeolite crystallinity are observed.
U.S. Pat. No. 3,442,795 to Kerr et al. describes a process for preparing highly siliceous zeolite-type materials from crystalline aluminosilicates by means of a solvolysis, e.g. hydrolysis, followed by a chelation. In this process, the acid form of a zeolite is subjected to hydrolysis, to remove aluminum from the aluminosilicate. The aluminum can then be physically separated from the aluminosilicate by the use of complexing or chelating agents such as ethylenediaminetetraacetic acid or carboxylic acid, to form aluminum complexes that are readily removable from the aluminosilicate. The examples are directed to the use of EDTA to remove alumina.
EP 0 259 526 B1 discloses the use of dealumination in producing zeolite ECR-17. The preferred dealumination method involves a combination of steam treatment and acid leaching, or chemical treatments with silicon halides. The acid used is preferably a mineral acid, such as HCl, HNO.sub.3 or H.sub.2 SO.sub.4, but may also be weaker acids such as formic, acetic, oxalic, tartaric acids and the like.
U.S. Pat. No. 4,388,177 to Bowes et al. discloses the preparation of a natural ferrierite hydrocracking catalyst by treatment with oxalic acid to impart catalytic activity for converting slightly branched as well as straight chain hydrocarbons in hydrodewaxing and naphtha upgrading. Increased activity is believed to arise from removal of iron, sodium and other impurities by such treatment.
It is known to use certain basic materials to deactivate the Bronsted acid sites on the surface of aluminosilicate catalysts. U.S. Pat. No. 4,520,221 and U.S. Pat. No. 4,568,786, Chen, et al., which are expressly incorporated herein disclose bulky amines, such as di-tert-butyl pyridine, as such basic materials.
U.S. Pat. No. 5,080,878 to Bowes et al., incorporated herein by reference, describes production of high viscosity index lubes by converting olefins over medium pore zeolites, e.g., ZSM-23, which are surface inactivated by contacting with aqueous fluorosilicate salt to replace external zeolite aluminum with silicon.
U.S. Pat. No. 4,870,038 to Page et al., which is expressly incorporated herein discloses the use of surface-inactivated zeolites such as ZSM-23 in olefin oligomerization processes which produce substantially linear hydrocarbons suitable for lubes or alkylating for preparing alkylbenzenes or alkylphenylsulfonates. The zeolites are surface-inactivated by contacting with bulky pyridine compound, e.g., 2,4,6-collidine.
The Young U.S. Pat. Nos. 4,301,316; 4,301,317; and 4,298,547, the entire disclosures of which are expressly incorporated by reference, disclose methods for using linear olefins, whereby these olefins are reacted with benzene in a particular way and then sulfonated to form biodegradable alkylbenzene sulfonic acid based detergents, particularly 2-phenylalkane sulfonates.